text:
Is it possible to suffer barotrauma during decompression?
Barotrauma is damage of lungs by air overpressure and may occur at overpressure as low as 30 kPa (4 psi). Overpressure in most aircraft is about double that value. So is it possible to suffer barotrauma when rapid1 decompression occurs? In an airliner or only in small airplane? And did it happen?
1If the decompression is explosive and the aircraft falls apart almost certainly, but it does not matter as all occupants will be dead either way. Only consider the case when the aircraft remains controllable.

if you are holding your breath, probably

I think you may be overestimating the power of "explosive decompression". Commercial aircraft pressurize the cabin to about 12 PSI. This is an extremely wimpy amount of pressure. A balloon is 16 PSI. A can of soda about 35. Letting the air out of a balloon would be a more dramatic event than a plane decompressing.

@TylerDurden, no, you are overestimating the durability of human lungs. If you had air from a 16 psi-balloon forced down your windpipe, it would tear your lungs to shreds. By the way, 12 psi is a bit too high even for absolute cabin pressure.

Briefly: yes, it's possible (but very unlikely); small pressurized aircraft are the more likely scenario; maybe it has happened but if so it's very rare.
According to the FAA's AC on Aircraft Operations at Altitudes
Above 25,000 Feet Mean Sea Level or Mach
Numbers Greater Than .75 it's possible and more likely to happen in a smaller pressurized aircraft:

(a) Explosive Decompression. A change in cabin pressure faster than
the lungs can  decompress. Most authorities consider any decompression
that occurs in less than 0.5 seconds as  explosive and potentially
dangerous. This type of decompression is more likely to occur in small
volume pressurized aircraft than in large pressurized aircraft and
often results in lung damage. [...]
(b) Rapid
Decompression. A change in cabin pressure where the lungs can
decompress faster than the cabin. The risk of lung damage is significantly lower in this decompression compared to an explosive decompression.

Unfortunately they don't cite any statistics or source for the statement "often results in lung damage" so it isn't clear when it has actually happened. Other sources suggest that it's very rare, for example Beyond the Black Box: The Forensics of Airplane Crashes says this:

The Air Force reports no serious injuries resulting from rapid
decompression with open airways, even while wearing an oxygen mask.
However, disastrous, even fatal consequences can result if the breath
is forcibly held with the lungs full of air. [...]
Lung damage is considered nearly impossible in a commercial aircraft
because of the large volume of air inside the plane. [...] Even Aloha
Flight 243 [...] did not decompress fast enough to cause internal
injuries.

In other words, it's not going to happen unless you hold your breath, but another source says that you won't be able to do that anyway:

I've had pilots tell me they would be able to hold their breath [in order to extend the time of useful consciousness]. That won't happen. First of all, the surprise of
the event will override any defensive measure you may have thought you
could put into place. Secondly, the rapid change in pressure
differential will make it impossible to hold your breath. (Remember,
we can be talking about a pressure differential of 8.8 PSI. Let's put
these pressure differentials into perspective. A differential of 8.8
PSI is 1267 pounds per square foot.

I think the surprise is a key point here: the flight or fight response increases your breathing rate so even if it were physically possible to hold your breath it's extremely unlikely that you would do so.
Interestingly, Google finds numerous sources that claim lung injuries are commonly caused by aircraft decompression, but I couldn't find any source that mentioned a specific incident or even any statistics on it. I did find one book that studied 47 incidents of aircraft decompression but there was only one single barotrauma event among them and it affected the ears, not the lungs.

Great answer, thanks. Apparently divers can suffer plumonary barotrauma by holding their breath and raising, so scuba diving trainees are explicitly warned not to forget to start breathing again after listening for incoming ships. So the last argument about not being physically able to hold the breath does not seem trustworthy (I understand it is made in answer to question whether one could hold their breath to extend their time of useful consciousness; for which the argument should have been no, you'd suffer barotrauma).

@JanHudec Diving is rather different: lung over-expansion injuries occur when the diver runs out of air, holds his breath and ascends. In that situation - underwater with no air - your instinct is indeed to hold your breath and that's what the training you mentioned tries to overcome. Because the decompression occurs gradually as the diver ascends, not suddenly as in rapid aircraft decompression, it's easy to hold your breath until you reach a dangerous point; this is very different from the sudden shock of an aircraft decompression. And indeed the context for the quote is extending TUC.

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text:
Under what authority can the AIM overrule the FARs?
A commonly held belief among pilots is that the FARs are regulatory, while the AIM is not. Violation of a regulation in 14 CFR is punishable by the FAA, while the AIM contains mostly "good ideas" and violation of its precepts is only punishable to the extent that it rises to the level of FAR 91.13 (careless and reckless operation). The FARs must be published in the Federal Register and generally be subject to the rulemaking process, while the AIM can be updated by the FAA at any time, with no input from anyone outside the Administration.
With that background, consider a note in the AIM, at the end of section 5-4-5(l) about Fly Visual approach segments, on page 5-4-20 (page 346 of the current PDF version of the AIM):

NOTE−
  The  FAA  Administrator  retains  the  authority  to  approve
  instrument approach procedures where the pilot may not
  necessarily have one of the visual references specified in
  14 CFR
  §
   91.175 and related rules. It is not a function of
  procedure
  design to ensure compliance with
  §
  91.175. The
  annotation  “Fly  Visual  to  Airport”  provides  relief  from
  §
  91.175 requirements that the pilot have distinctly visible
  and identifiable visual references prior to descent below
  MDA/DA.

This is, as far as I can tell, the only location where this exemption from FAR 91.175 is described. FAR 91.175 is quite specific in the elements needed before continuing beyond the DA/MDA, and does not stipulate that the Administrator has the authority to authorize exemptions. For an example of one that does, consider FAR 91.117(a):

Unless otherwise authorized by the Administrator, no person may operate an aircraft below 10,000 feet MSL at an indicated airspeed of more than 250 knots (288 m.p.h.).

What authority gives the AIM the ability to carve out an exception to the FARs? Are there other situations where the FARs are contradicted by a non-regulatory document without explicitly allowing exemptions or authorization by the Administrator?

I don't see how the AIM overrides FARs in this example.

@acpilot The FARs say you need specific objects in sight before continuing past the MAP. The AIM says, "never mind that, in this situation we're making an exception to the rules."

@NathanG That's not what the AIM says here. The AIM says the FAA retains the authority to authorize exceptions to §91.175 as made explicit in the opening line of §91.175: Unless otherwise authorized by the FAA...

I don't understand the question.  Does the law state that there are other sources for aviation law?  If so, fine.

The issue you have appears to be that the AIM describes a case where procedures don't follow a rule (91.175) and you don't see where the authorization comes from for that deviation.
What you're missing is that the approach procedures are in fact rules themselves.  They just don't get published in Title 14 CFR.  Standard instrument procedures are covered by Part 97, Subpart C.  It essentially states that the procedures are controlled via the FAA Order 8260 series.
So if the approach procedure specifies minima or other procedures outside the norm of a separate rule, the procedure is the controlling rule.

The AIM cannot, and does not, overrule the FARs (14 CFR). The example highlighted in the question is not an example of the AIM contradicting 14 CFR; rather this is an example of the AIM reminding pilots that the FAA retains the right to authorize certain exemptions to 14 CFR, in this case as made explicit by 14 CFR 91.175. As mins' answer accurately affirmed, the AIM is—in fact—not regulatory.

The clarification needed for this question, toward which Gerry directed our attention, is that authorized procedures are authorized under one of the subchapters of 14 CFR, Chapter I, not the AIM.
In 5-4-5(l), the AIM affirms that the FAA retains the authority to authorize exceptions to §91.175—as made explicit in the opening line of §91.175:

(a) Instrument approaches to civil airports. Unless otherwise authorized by the FAA, when it is necessary to use an instrument approach to a civil airport, each person operating an aircraft must use a standard instrument approach procedure prescribed in part 97 of this chapter for that airport.

One example of approved instrument approach procedures (IAPs) not prescribed in
§97.20, are the IAPs authorized for specific Air Carriers. Many Air Carriers—companies with an Air Operator Certificate (AOC), such as a charter company operated under §135 or an airline operated under §121—can and do have their own IAP that the FAA has authorized. Such IAPs will be included as part of the Operation Specification of the company's operating certificate, and will thereby be authorized under §119.
The FAA has the authority to authorize any individual or company to perform any IAP. While I don't know of any specific examples of this, theoretically, this could take the form of a Letter of Authorization (LOA) allowing a Minnesota farmer to perform an IAP of his or her own design to the farm's grass strip. The FAA retains the right to authorize IAP; some paths to that authorization are better defined than others.

In the aeronautical information manual (AIM) itself:

This publication, while  not  regulatory, provides information
  which reflects examples of operating techniques and procedures which
  may be requirements in other federal publications or
  regulations. It is made available solely to assist pilots in
  executing their responsibilities required by other publications.

From that:

AIM is not regulatory.
AIM is aimed to assist pilots in executing their responsibilities.
Pilots responsibilities are described in other publications.

A few paragraphs below:

The FAA publishes the Code of Federal Regulations (CFRs) to make
  readily available to the aviation community the regulatory
  requirements placed upon  them.

FAR = Title 14 of CFR.

Precisely to the point, the AIM is not regulatory.

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sort: votes


text:
May pilots perform FMS database updates under Part 135?
Are pilots allowed to perform FMS database updates under part 135?  If so, do they need formal training entered in their pilot records before they are allowed to do it?

Updating a navigation database used to be considered preventative maintenance and was required to be performed by a mechanic under Part 135.  However, the regulations were changed at the end of 2012 (here is the final rule) and it no longer falls under this category so pilots are allowed to update "aeronautical databases" (a new term) if it is "easy" to do (see the regulation quoted below for the exact requirements).  There is no training requirement specified by the regulations, however there may be company specific procedures which require it.
14 CFR 43.3 was updated, and now says (in part):

(k) Updates of databases in installed avionics meeting the conditions
  of this paragraph are not considered maintenance and may be performed
  by pilots provided:
(1) The database upload is:
(i) Initiated from the flight deck;
(ii) Performed without disassembling the avionics unit; and
(iii) Performed without the use of tools and/or special equipment.
(2) The pilot must comply with the certificate holder's procedures or
  the manufacturer's instructions.
(3) The holder of operating certificates must make available written
  procedures consistent with manufacturer's instructions to the pilot
  that describe how to:
(i) Perform the database update; and
(ii) Determine the status of the data upload.

There is a difference in language that various parts of the FAA use. What is described here as updating the database, is elsewhere (AC20-153A) described as loading the database.

@DeltaLima Ummmm, okay....?  (Does that change something?)  That AC is for people processing aeronautical data (ie creating databases).  It was also written in 2010 before the change to the regulations.

I assume that by updating you mean loading a pre-compiled database into the FMS, replacing the old one.
The RNAV database inside the FMS should be updated according to the 28 day Aeronautical Information Regulation and Control (AIRAC) cycle. Typically this is a maintenance task and the pilot has no play in this. Of course if the pilot also holds the required maintenance certificates, then he can update the database in the appropriate way. However, he is not acting in his capacity of pilot in that case, but wearing his maintenance hat.
In some cases the database update is not considered maintenance and can be performed by the pilot. 14 CFR Part 43 covers Maintenance, preventive maintenance, rebuilding and alteration. It contains an interesting section regarding databases; 14 CFR § 43.3(k) specifically addresses database updates.

(k) Updates of databases in installed avionics meeting the conditions
  of this paragraph are not considered maintenance and may be performed
  by pilots provided:
(1) The database upload is:
(i) Initiated from the flight deck;
(ii) Performed without disassembling the avionics unit; and
(iii) Performed without the use of tools and/or special equipment.
(2) The pilot must comply with the certificate holder's procedures or
  the manufacturer's instructions.
(3) The holder of operating certificates must make available written
  procedures consistent with manufacturer's instructions to the pilot
  that describe how to:
(i) Perform the database update; and
(ii) Determine the status of the data upload.

If these conditions are not met, then there is a final escape door which might apply to Part 135 rotorcraft pilots:
14 CFR § 43.3(h) states:

(h) Notwithstanding the provisions of paragraph (g) of this section,
  the Administrator may approve a certificate holder under Part 135 of
  this chapter, operating rotorcraft in a remote area, to allow a pilot
  to perform specific preventive maintenance items provided—
(1) The items of preventive maintenance are a result of a known or
  suspected mechanical difficulty or malfunction that occurred en route
  to or in a remote area;
(2) The pilot has satisfactorily completed an approved training
  program and is authorized in writing by the certificate holder for
  each item of preventive maintenance that the pilot is authorized to
  perform;
(3) There is no certificated mechanic available to perform preventive
  maintenance;
(4) The certificate holder has procedures to evaluate the
  accomplishment of a preventive maintenance item that requires a
  decision concerning the airworthiness of the rotorcraft; and
(5) The items of preventive maintenance authorized by this section are
  those listed in paragraph (c) of appendix A of this part.

Summary
When the database update meets the conditions stated in paragraph (k) of  14 CFR § 43.3 it is not considered maintenance and may be performed by the pilot.
When  CFR § 43.3 (k) conditions are not met the pilot cannot perform the update unless the Administrator approves it under 14 CFR § 43.3(h).


text:
Do cargo operators need an AOC?
Is it just commercial operating aircraft flying paying passengers that require an air operators certificate (AOC) or do cargo operators require one also?

You need an AOC except in very rare circumstances.

An aircraft doesn't need an AOC    Operating the aircraft for anything other than for private purposes is why you need one.

I think you need a comma in there...

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text:
IFR Currency with a safety pilot who has a BasicMed
Here’s my situation and question.  For my IFR currency, I’ve asked a friend to be the Safety Pilot.  He’s aptly qualified BUT he does not have the traditional Medical, but rather he has BasicMed.  My question is; Can I still use him as a Safety Pilot, without jeopardizing my IFR Currency?  If he’s deemed PIC, can I still claim the time and use the IFR work (approaches, hold, tracking, etc…) for my IFR currency?

Due to a quirk in the Basic Med rules, he can only act as a safety pilot if he is PIC—which is fine. Logging time doesn’t depend on being PIC, only on being the sole manipulator of the controls.

Related: https://aviation.stackexchange.com/questions/42989/how-does-the-faa-basicmed-affect-the-safety-pilot-for-somebody-flying-under-the

FAR 61.113(i) authorizes flight as PIC when using BasicMed. Therefore, your buddy can act as safety pilot if he is also acting as PIC.
If you were acting as PIC, that would make your buddy SIC (as a required crew member), which still requires a traditional medical certificate.

He can be PIC but not SIC???

@DJClayworth Correct. BasicMed only allows flying as PIC, not SIC, as strange as that seems. Laws are not required to make sense.

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text:
How to monitor MSA sector from an RNAV waypoint in the 737?
For instance, at Manchester (EGCC) the approach procedure for RNP 23L has the MSA based off of RNAV waypoints; DOMIG bearing 142 to 322, OSNAP bearing 322 to 052, TINVA bearing 052 to 142.
From NATS UK:

If you were flying this approach how do you determine which MSA sector you are in? Is there a way in the FMC to see real-time your bearing and distance from a given waypoint (like you would do traditionally with VOR and NDB needles)? Or do you just have to use common sense and the ND to approximate it?
Likewise some airports use the ARP as the reference point for MSA, how would you know which sector you're in?

Serious question: how would that knowledge affect how you operate the aircraft?  ((I've briefed lots of MSA numbers, but never cared about any of them after that. Of course, EGPWS is a great security blanket that way.))

@RalphJ the safety net is not a hammock. If you rely 100% on EGPWS to keep you out of terrain, the day that EGPWS fails you will have an encounter with cumulus granitus. There is no excuse to not be aware of the MSA and bust it. In those few rare cases that it is busted, EGPWS may safe the day, but please don't assume that EGPWS is infallible.

@DeltaLima Flying the altitudes on the instrument procedure (which absolutely can be below Min sector altitudes) will keep you safe. EGPWS is a great tool for situational awareness of terrain - far far better than MSA quadrants are - and a magnificent safety enhancement, but it's never the primary navigation. Min sector altitudes, IMHO, have extremely limited utility. Those are distinct from each leg's min safe altitude, which I agree are sacrosanct, even if EGPWS looks clear.

@RalphJ I am glad that we are on the same page with respect to adhering to minimum safe altitude! I interpreted MSA as Minimum Safe Altitude (which is used in ATC monitoring & warning systems such a MSAW ) instead of MSA as Minium Sector Altitude, which is indeed a very conservative measure based on 1000 ft clear of the highest obstacle in a 25NM radius.

@DeltaLima  Definitely doesn't help clarity when the same "MSA"acronym is used for two distinctly different, though not entirely unrelated, concepts! My initial comment above was, as I believe the OP was, using MSA in the "sector" version... which I've often briefed (it's a standard part of the brief where I fly) and never used. I agree w your answer below; overall situational awareness matters; knowing the point that we cross into "this" sector, not so much.

I think there is a misunderstanding in the question: while the distances are off of the 3 IAFs, the bearings are all off of the same point, C23LI. And, those are TAA's, not MSA's. The MSA is 3,500', centered around the MCT navaid, and has no sectors.

@RalphJ Good catch! I didn't look at the chart when I wrote the answer yesterday. I updated the answer to include that info.

There is a way to do this in a 737NG using the FMC FIX page:

1 FIX Name
Enter the desired fix.
Valid entries are airports, navaids, waypoints or runway identifiers from the
navigation database. [...]
3 Radial Entry (example)
Enter a radial from the fix. Radials are displayed on the navigation display map
mode as green dashed lines from the fix.
When the radial intersects the active route, the ETA, DTG, and predicted altitude
at the intersection are displayed. [...]
6 Radial/Distance From Fix (RAD/DIS FR)
Displays the radial and distance from the fix to the airplane. This information is
continually updated as the airplane position changes.

(Boeing 737 NG FCOMv2 11.42.57 - Flight Management, Navigation - FMC Cruise)
For your Manchester example you would define 4 fixes:

C23LI: The radials are all based off this waypoint, so you would enter 142/, 232/ and 322/ into LSK 2L to LSK 4L to draw green dashed lines for the three sectors onto the ND, which makes it easy to see in which sector you currently are (or if you are approaching a different sector).
DOMIG, OSNAP and TINVA: The distance of 25 NM is based off these waypoints. You can optionally draw green circles around each of them by entering /25 into LSK 2L on each fix page.

Additionally, the radial and distance information is continuously displayed at the top of the fix page. You would just have to cycle to the correct fix using the NEXT PAGE and PREV PAGE buttons.
Since the fix page also allows airports as a FIX Name, this will also work if the MSA is given around the airport reference point.
Having said this, I don't think any operators actually teach their pilots to do this. As Ralph J said in a comment above, there is really no operational need to do so. While on the approach (or transition, or missed approach), the altitude constraints on the waypoints will keep you safe. When under radar vectors, the limiting altitude is MRVA (minimum radar vectoring altitude), which can be lower than MSA anyway.

Good info, but why wouldn’t you simply reference ownship position on the MFD map?

@MichaelHall That's what I would do, I'm just saying you can draw these lines, if you really want to. And of course there are airports with more complicated MSA sectors than Manchester (usually in very mountainous terrain).

I would just suggest that you lead off with what you would do then.  A screenshot of the superior SA of the MFD map would be bonus points.  Because the way I read this was like “how can I undo this bolt, can I use visegrips?”  And the answer focusing on how to adjust visegrips to avoid stripping while avoiding the obvious first choice of using a wrench.

The short version is that, when the MSA is a TAA like this, you will always be given the IAF that is the basis for the sector you are in (or are approaching).
For instance, if you are due west of the airport, you would be “cleared direct TINVA, cleared RNP 23L approach”. You then look at the TAA sector for TINVA and see the MSA is 3500, so as soon as you are within 25nm (if not already), you could descend to 3500 in preparation for the approach. You would also have that approach (including the selected IAF) set up your FMS, which will always show your current distance and bearing to the next fix, so you could verify you are within the appropriate sector until you pass TINVA, and after that it doesn’t matter since you’re established on a segment of the approach.
There is nothing here specific to any model of aircraft.

I would say you use the ND and general situation awareness to judge your position.
For the Manchester/EGCC case, the three reference RNAV waypoints are all IAFs. They are laid out in standard fashion, with the MSA as described in your post clearly describing the 10 x 5 NM area spanned between them. I don't think you need the FMS to measure the angles, just a brief look on the navigation display should do it. I guess you know your position w.r.t. the IAF during the approach.

If you were flying this approach how do you determine which MSA sector
you are in?

While some people are very adept at processing digital information and creating a mental image in their brain, for most people a visual display is superior in providing almost instantaneous situation awareness.  Modern multi-function displays, (MFDs) have a map mode that performs this function quite well.
Once an approach is loaded, (unfortunately the example image below on the right side MFD does not show the same approach as depicted in the question) it should be a simple matter of orienting your ownship position relative to the MSA/TAA quadrants shown on the approach plate by taking a quick glance at the map.
If you wanted to be precise and had time you might figure a way to draw additional lines on the display, but it really isn't difficult to imagine a dividing line on the map and determine whether it is forward or behind you.


text:
How are altitudes handled with airports near or above transition altitude?
Transition altitude refers to the altitude above which all altimeters are set to a standard pressure setting (typically 29.92 inHg) instead of to the local surface pressure, and altitudes are given in flight levels (the standard-pressure altitude, divided by 100; for instance, with one’s altimeter set to standard pressure and reading 52,900 feet, one would say “flight level 529” rather than “52,900 feet”) rather than in feet above mean sea level (MSL).  The height of the transition altitude depends on where you’re flying; for instance, transition altitude is at 18 kft in the United States, 10 kft in Australia, and as low as 6 kft or even lower in parts of Europe.
Low transition altitudes raise the possibility of an airport’s height above sea level being close to, or even above, the transition altitude; this wouldn’t be an issue in the United States (where only the very highest one or two mountain peaks reach above the 18-kft transition altitude, and this altitude is well into the Death Zone anyways unless one is exceptionally well-acclimated to very high altitudes) or Australia (where even the highest peaks are less than 8 kft above MSL, well below the 10-kft transition altitude), but could easily become a problem in regions with both high terrain and low transition altitudes (such as Europe, which has many high mountains - and, more to the point, many airports high up in mountainous areas - combined with transition altitudes that go at least as far down as 6 kft), as maintaining terrain clearance requires knowing what one’s altitude actually is, rather than knowing what altitude the pressure at the static ports would correspond to if the local altimeter setting was 29.92 inHg.
How do airports located at elevations near to, or above, transition altitude handle this?  Does the airspace around these airports use a local transition altitude higher than elsewhere?  Do approaches and landings at, and takeoffs from, these airports rely solely on radar, rather than barometric, altimeters?  Something else?

Related Why isn't transition altitude standardized in Europe? and Why are the transition altitudes/levels different around the World?. Both have links to this Eurocontrol summary.

I don't have an authoritative source for what the various regulatory agencies in the various regions use for publishing their transition altitudes, but your assumption is pretty close: airspace is planned so that no airport is "that close" to the transition level.
Some TAs are defined across large swaths, such as the US, Canadian, Australian TAs.  Some TAs are more broken up, even within political boundaries.  I believe Brazil (or at least one of the South American countries) has different TAs for different "terminal areas".
There has been on-again/off-again discussions in the European region of establishing a common TA, but (as of this date) that has not happened.  You will see fairly low TAs in low, flat areas like The Netherlands, but higher TAs in the mountainous regions.
Again, all of these TAs are "planned out" so that there is no danger of being too low while assigned to a flight level, and so that you are back on QNH well before you are on approach to an airport.


text:
Can I check my density altitude with brake tension?
The same way one would apply the brake and accelerator, the more torque the more break is needed to hold the car, can a plane use this same technique to check the plane thrust and air density before take off?
Using a brake pressure gauge, could density altitude be measured by how much pressure is needed to hold the plane in place?

You would have to have a brake pressure indicator that shows the pressure being applied to the calipers, where you could observe the minimum pressure required to hold the plane when WOT, and some charts or calculations that showed the static thrust being produced with a given amount of brake pressure.  But then the amount of pressure varies with a lot of things, how wet they are, how worn they are etc. etc.  An awful lot of scatter.
If you really wanted to do that sort of thing, the most practical thing to do with a reliable amount of precision would be to carry along a force gauge (digital fish scale more or less) with a bit of rope and tie the plane to a fence post with the force gauge and do a brief full power run and measure your static thrust directly, then interpolate performance based on that.
I don't know of anybody that's ever done that, ever.  Why bother when the manufacturer has already tested all the permutations and conditions and produced performance charts, and all you need to do is plug in the numbers on the charts and follow the little lines to get reliable, conservative values.

I like your answer because I did not thing of using a spring scale in that way.

I should have added the people HAVE done that for the purpose of measuring static thrust for experimental or data gathering purposes, just not as a procedure for determining TO performance.  Search YouTube and you'll find videos of guys doing that to find out how much static thrust their homebuilt or ultralight is making, mostly out of curiosity.

Thank You for saving a dumb question from my CFI.

That wasn't a dumb question at all.  Making the connection between thrust and brake holding power and using brake pressure as a way to evaluate thrust as a concept means you think out of the box and that's not a bad thing at all. In my years in the aerospace business I've participated in many brain storming sessions trying to solve technical problems, where those sorts of things were put forward and explored.

You may be able to get a rough estimate of if your engine is producing sufficient thrust utilizing brake pressure. But, how will you determine how much thrust is being produced? Your brakes are not calibrated so carefully as to adequately determine that. You would only be guessing. You might get a better indication of engine performance by utilizing the sound of the engine.
The best way to tell if your engine is producing enough power with a fixed pitch prop is using your tachometer. One is required for all flight in a powered civil aircraft with a standard category U.S. airworthiness certificate in the US by 14 CFR 91.205. With a constant speed prop, you are required to have a manifold pressure gauge to indicate the power output of the engine.
On the other hand, even if you could judge your engine output without instruments, it still would not account for the effect of density altitude on the lift producing airfoils. Instead, you are better off determining density altitude using the weather data that you should have reviewed during your preflight planning required by 14 CFR 91.103. For that, you need no aircraft instruments.


text:
So fast, it melts the ice off?
Approximately, how fast would an aircraft have to travel through freezing air to melt the ice off the wing, propellers, or rotor blades?

Couple more variables you'll probably need: Altitude (alternatively, air pressure), and dew point.

Please confirm you mean "melt" as opposed to just 'get rid of...'.  Because ice will sublimate at pretty low speeds if the air is dry.  Also, temperature is a key variable.  "Freezing air" can be 32F down to absolute zero.

Longer than a minute, less than an hour.  That's about as precise an answer as you're going to get with so many variables.

As already done in this answer, we can calculate the True Air Temperature (TAT) that the aircraft's skin will feel from the Static Air Temperature (SAT) and the Mach number:
$$ \frac{\text{TAT}}{\text{SAT}} = 1 + \frac{\gamma - 1}{2} M^2 = 1 + \frac{1}{5} M^2 $$
(using $ \gamma = 1.4 $ for air). For different SATs the curves then look like this:

I added a dashed line at a TAT of 10°C because this is the limit defined for icing conditions. At higher TATs, the ice should definitely melt (although it could already start melting before). We can now obtain the intersection Mach number as a function of SAT by inverting the formula above:
$$ M = \sqrt{5 \left( \frac{\text{TAT}}{\text{SAT}} - 1 \right)} $$
The resulting curve looks like this:

As you can see, a Mach number between ~0.4 and ~1.3 will be required to melt ice, depending on the SAT.


text:
Engineless Blimp Navigation System
I understand wind direction can vary in a column of air? With only altitude control on a blimp to navigate for long flights, a blimp in theory could navigate without engines. In order to take real time wind direction reading along a column of air with reusable devises like a fishing line, weighted for stability, then a sensor or string be used to get an accurate reading? or maybe a cluster of spread out drones could be used for this?

Balloonists already navigate like this.  For typically short flights, it's enough to check the "winds aloft" forecast just before launch;  no in-flight sensing is needed, beyond direct observation of which way the balloon is drifting.

@CamilleGoudeseune i corrected it thanks for the help

Yes, this gets into the question of off-board versus on-board far-field air data sensing capabilities. With regards to the latter, lidar systems have been studied. Alas, ttbomk, no practical, reasonably-priced system solution exists. However, conceptually, multiple off-board near-real-time sources could be leveraged. The choice might be determined by intended altitudes of operation. For example, there may be a way to 'crowdsource' derived wind data from other aircraft operating in the region. Another possibility is satellite-based sensing, such as that provided by Spire.

To check the wind speed and direction at levels below the aircraft, balloon pilots often drop whipped cream or shaving cream.
To explore the wind speed and direction at levels above the aircraft, releasing small (toy) helium balloons would be a good option-- certainly balloonists routinely do this from the ground before launch to see what is going on higher up.
Of course these days the obvious solution (as hinted in the question) is an array of drones (e.g. quadcopters) autonomously keeping station at various positions above and below the balloon/ blimp--data such as power demand, required angle of tilt relative to the horizon, and GPS-derived vertical and horizontal groundspeeds could be utilized to map out the vertical and horizontal shears in the wind field above and below the balloon/ blimp.


text:
Flying using less fuel in one tank
Can flying using fuel from one and not the other tank save fuel from constant cross winds over long flights or make it easier to land?  Is there anytime where having the ability to shift the weight of the plane using fuel imbalance helpful?

What do you mean by save fuel during crosswinds?

Re "What do you mean by save fuel during crosswinds?"  -- exactly.  Does original poster not understand that crosswind correction during cruise actually doesn't require any sustained displacement of control surfaces?

@GdD is there anytime where having the ability to shift the weight of the plane using fuel imbalance helpful?

If anything, flying with one tank full and one at, say, 1/2 empty will increase drag, because of the aileron displacement required to offset the lateral imbalance, plus a small rudder input to compensate for the aileron input.
Technically if you want to sideslip very slightly on landing, a significant imbalance would reduce or eliminate the aileron input required to maintain the slip and you might only need to apply rudder, but that would maybe help you for about 5-10 seconds. The rest of the time you are holding aileron to keep from rolling (unless you have roll trim).
In other words, the imbalance is just an annoyance about 99.5% of the time.

I suspect this pilot might have preferred a fuel imbalance.

Holy crap look how little aileron he has in.  Fuel transfer no doubt helped!


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How to determine the maximum forward airspeed of a plane in an unaccelerated flight?
What is the equation needed to determine the maximum forward airspeed of a propeller driven plane in an unaccelerated level flight? I need an example with units of measurements.
The engine is rated at 55-75 hp.

@quietflyer does this help?

Thrust reduces with speed and drag (normally!) increases with speed. The maximum speed is the one at which the thrust and drag curves intersect (T = D). Sophit's answer explains well how to mathematically determine that speed.

EDIT: I added a calculation at the end of the answer

Thrust $T$ produced by a propeller is:
$T=\eta \frac{P}{V}$
where $\eta$ is the propeller's efficiency, $P$ the power supplied to the propeller and $V$ the flying speed.
This thrust wins drag, which can be as usual expressed as:
$D=½\rho V²SC_d$
where $\rho$ is air's density, $S$ wing surface and $C_d=C_{d_0}+\frac{C²_l}{\pi Ae}$.
$C_l$ can be derived from the usual equation for lift $L$ that equals weight $W$:
$L=½\rho V²SC_l=W \Rightarrow C_l=\frac{W}{½ \rho V²S} \Rightarrow C²_l=\frac{W²}{(½ \rho V²S)²}$
Substituting and equating $T=D$ we get:
$\eta \frac{P}{V}=½\rho V²S(C_{d_0}+\frac{W²}{(½\rho V²S)²(\pi Ae)})$

So far so good.
This equation can be obviously solved mathematically but a graphical representation is easier; we just have to plot that equation after having rewritten it as:
$0=-\eta \frac{P}{V}+½\rho V²S(C_{d_0}+\frac{W²}{(½\rho V²S)²(\pi Ae)})$
This equation is 0 where it intersect the x-axis and that intersection is the $V$ we are looking for.
Let's use then the values given in the question:

$\rho=0.96kg/m³$; I really couldn't convert the given $q$ in a standard number so I use the ISA density at 1'500m (5'000ft).
$S=3.5m²$.
$C_{d_0}=0.021$
$\eta= 0.8$; this value is ok if we consider a variable-pitch propeller or a propeller working at its design point; otherwise it can be as low as 0.4 or even less.
$P=56'000W$ (75hp).
$W=3'700N$.
$A=7.65$.
$e=0.821$.

Substituting we get:
$0.0355V²-44'800/V+110.81/V²$
whose graphical solution is some 108m/s 210kts (general shape in the first picture and zoom of the solution in the second picture):

Just out of curiosity, with an $\eta=0.4$ the speed reduces to some 85.8m/s 167kts.

To be clear: V is measured knots? P is measured in Horse Power? p (air density) is measured in... This is why I need an example with the unit of measurements. If I strickly use SI units will it come out correct? +1

@Justintimeforfun Here's a suggestion: Convert everything in SI units - V in m/s, P in watts, ρ in kg/m³, S in m² and so on.. After calculating the V, you may convert it back in the units you would desire (knots). Yes, if you strictly use SI units, your answer will be correct. But! this V is TAS. To convert it into IAS (which I believe is what you want), you will first need to calculate the dynamic pressure (the SI unit of which is N/m² or pascals). Then from there you can finally convert it into IAS.

@AdityaSharma is correct. Just an example about power: horse power is a unit of measurement which is not tied to anything else; on the other hand, Watt is 1kgm²/s³ and it does show a tie with the units it derives from (supposedly a mass, an acceleration and a speed)

@RobertDiGiovanni: because I think it's against the policy of Stackexchange doing someone else's homework

@RobertDiGiovanni: I gave the bricks and the instructions how to assemble them; I let the others play Lego ;)

even when using metric system it's good to do a units check.. often times you end up with things like gas constant for air being R=0.287 or 287 "units" depending on where you look it up, and in results like reduced turbine mass flow being sqrt(R)*xysomething .. you're off by a factor of 31.something, not necessarily obvious you missed a kJ vs J

"Do" is an expression in your solution -- is it a "given" in the problem?  Also, Cl appears to be treated as constant in this answer.  If that's not the intent could you perhaps make more clear which value of Cl to use?

@RobertDiGiovanni: thanks for your kind comment

@quietflyer: you're definitely right, I should replace $C_l$ with its value that depends on weight and dynamic pressure but then we get a definitely more complicated equation in $V$... let me see if I can somehow simplify it.

@quietflyer: done

Can be rearranged to solve for V$^3$.  Your calculated Cd0 + Cdi came out to (a believable) 0.027.  The real rub is efficiency × Power is proportional to V$^3$.  But excellent work (both writers) for working through those numbers.

Your "givens" include a table of Cl/Cd versus airspeed.
Therefore it is simple to prepare a graph of Cd/Cl versus airspeed.
From this, you can prepare a graph of (Weight * (Cd/Cl)) versus airspeed.
Thrust Required = Weight * (Cd/Cl).  So this is your graph of Thrust Required versus airspeed.
You'll also need to prepare a graph of Available Thrust versus airspeed.  For this, you'll need to know more information than you've given us.  For example, you might have a curve of engine horsepower versus RPM, along with some indication of prop efficiency.  Or you might even have some way of measuring thrust delivered by the motor to the prop in actual flight.  Without knowing more about what your "knowns" are, it's hard to be specific about how you should prepare the graph of Available Thrust versus airspeed.  (It's going to make a tremendous difference whether the propeller is fixed-pitch or variable-pitch (constant speed), and if the former, for what airspeed it is optimized -- i.e. "climb prop" versus "cruise prop".)
An absolute upper bound for your Available Thrust at any given airspeed would simply be Power / airspeed, assuming that the full nominal value of (75 hp?  It's unclear what "55-75 hp" means) is available regardless of airspeed.  You'll never have this much thrust available in actual practice, but it's a starting point.
At any rate, the airspeed (well to the right on your graphs, i.e. well above the minimum-thrust-required airspeed) where the Thrust Required curve crosses the Available Thrust curve, is the maximum sustainable airspeed.  If you've used the theoretical "upper bound" expression for Available Thrust given above, this airspeed figure will be overly optimistic.  (But if this was a homework problem, perhaps this is the approach you were expected to take.)

Can you do this in Horse power (propeller) not thrust (turbine)? +1

An example would help so much.

Thrust of a propeller is power divided by speed. The power being the effective power delivered by the propeller, so engine power times any transmission and propeller efficiencies (which vary with speed to some extent).


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What plane cost less per mile to operate for one person?
The 98 Toyota Corolla has a strong history for being a low maintenance, fuel efficient and cheap car. 400k mile reliability if driven with respect and preventative maintenance.
What plane has these qualities with at least a 450 mile range? So I can fly back and forth to flight school instead of driving.
I am sure there are many that will fit the bill but I am looking something for beginners and the cheapest way to fly myself.
Second Scenario: Suppose only using the basic maintenance, without anything more than an oil/filter etc., which plane would last the longest. Obviously simpler plans require less money per nautical mile; of those which would last the longest?

I think this question is way too broad, and will be heavily dependent on opinions.  There are plenty of online discussions out there on choosing a GA light piston aircraft, this isn't the place to rehash the subject.  Voting to close.

Airplanes don't measure their use in miles (for a lot of reasons which flight training should make clear), but in engine & airframe hours - that is, the "Hobbs" meter: https://en.wikipedia.org/wiki/Hobbs_meter

A basic plane is more reliable than a more complex plane. A small 4-cylinder engine is more reliable that a larger engine. For thoese reasons I tend to think that a basic, all-metal plane like a C150 or even Cherokee 140 is safe bet (though the 140 has a larger engine).  If you are normally always VFR with light winds an old tailwheel like a Cessna 120/140 or Champ/Chief could work.  Planes of that era may not have the range you want though.  The trip will pe painfully slow with every option I've listed, too.

@acpilot This is a good answer I would also upvote. I have to come home on the week ends and I would rather fly that trip than drive it. Of the plains you listed which will cost less to keep?

@acpilot A complex plane can be way more reliable than a basic plane. The A350XWB can probably do over 100 million miles, between its carbon fuselage, well-proven systems, and high availability (the 787 was a bit more experimental, so might not hit the sweet spot). And across the fleet it will take billions of miles between accidents. Nothing GA will ever come close.

It goes without saying that we are scoping for GA.  Sure, a brand new airliner serviced by a staff of professional mechanics with a practically unlimited budget might have a higher dispatch reliability than a 1946 Aeronca Chief with a 2400hr C-65.

@Justintimeforfun - they're all cheap to operate. I think a C150 works best. All metal, everyone knows how to maintain an O-200, almost every single A&P has some level of familiarity with Cessnas, parts are everywhere, etc. The fabric planes need new fabric every 20 or so years. Tailwheels might cost a little more to insure. The C150 is just about as basic as it gets while retaining just enough "extra" to be practical...just barely.

The most reliable aircraft is the one that is maintained the best, and the simpler an aircraft is, the easier it will be for you to afford to maintain it properly—both because it will need less maintenance in the first place and because it'll be cheaper to buy, insure and fuel, leaving more of your funds available for maintenance.
However, the premise of flying to/from a flight school seems fundamentally flawed. You are almost certainly going to need to store your plane at an airport, and if so, you should get instruction at that airport rather than fly somewhere else for it. You won't be allowed to fly any significant distance (i.e. enough to justify flying rather than driving) alone anyway with just a student pilot license.

The flight school has aircraft student parking.

How far away is your flight school?  Have you been signed off to solo yet?  (You said you were a "beginner"...)  And may we assume you've bounced this plan off your CFI and he/she approves?

@Justintimeforfun - I think you are missing StephenS’s point. Where will the aircraft be based? Is it your home airport? Or, is it your school airport? You will need parking at both locations. Depending on where you are, one month’s hangar rental alone in one location could cost you anywhere from 2 to 10 full tanks of gas in your car. If you plan on living at home and flying to school every day, it would cost you less to get lessons at your home airport. And, I f you do not have a PPL, a CFI might not endorse your solo flights for commuting purposes. They will be liable.

On the other hand, if you only plan to make the round-trip flight once a month or even once a week, this would be a fun way to build time. Overnight parking at another location away from school might run $5-20 a night in outdoor tiedown fees. And, your CFI might feel more comfortable endorsing you for an occasional solo flight on a flight by flight basis until you get your PPL. Be aware that the CFI will probably place very stringent requirements on the endorsement (only to listed airports, along listed routes, in almost perfect daytime weather). And, you may still have to drive in some days.

In the US, a student can't fly solo more than 25nm from their "home" airport without a CFI endorsement for each flight. And driving will be faster for anywhere that close

@DeanF. 390 mile from my house to the school. How much more would it cost compaired to a car? The school has a student runway and parking once a week round trip sound good.

@StephenS I do plan on getting my private license first before commuting to and from school.

@Justintimeforfun - Well, just by quick math, more than twice as much. I could drive that trip in 6-7 hours on 1 tank of gas costing me 30-45 dollars a tank depending on fuel costs. I could make that same trip in 4 hours on 40 gallons of fuel in a C172. But, at 4-6 dollars per gallon of avgas, that would total out to 200 dollars per one-way trip for gas alone. You still have to factor in maintenance on the aircraft, oil changes every 25-50 hours, hangar fees away from school, annual inspections, etc. You could reduce the fuel cost to 120 dollars per one-way trip in a SportsCruiser.

Also remember, any day that you make the one-way commute, you should not have a flight lesson regardless of if you travel by car or by plane. Practice doing an IMSAFE checklist before every commute trip just like you should before every flight. Really, you should be doing a full PAVE and even NWKRAFT before each commute. The A in PAVE can stand for automobile.

@Dean F.: You could also get a plane with a mogas STC, and pay half as much for gas.

@Justintimeforfun, i assume that 390 miles is nautical flying miles.  How many statute driving miles, and what kind of speed limit?  To make a fair cost comparison you need to convert to the same unit of measure for distance, then figure time and fuel burn.  As well as other costs, including the value you put on your personal time.  But, if you are serious about pursuing your commercial ticket and would be spending money anyway to drive that far it would be a great way to rack up flight time.

@MichaelHall you right strait line miles for plane minus wind... Is it worth the extra cost to save an extra few hours a week? I'm not thinking of how to get an engine to run on 87 which many planes can. So fuel is not of concern and parking is not of concern. Now cost of purchasing a plane and up-keep is. Maybe flight time.

@jamesqf - True. But, after seeing the aftermath of 2 vaporlock crashes linked back to mogas usage, I am leery of using it. At least where I live. One of the schools where I rent has prohibited the use of mogas in their mogas fleet. If you did use mogas, a 6 gallon/hour fuel burn would give you a 50° reduction in fuel cost for a 25-40° decrease in commute time. There is still the costs of ownership to consider. I doubt you could offset that by not owning a car. How would you get to the airport, after all .

@Justintimeforfun - As Michael Hall has said, if you have the money for aircraft ownership, and just want a way of time-building possibly cheaper than renting, then go for it. Just make sure flying is not your only means of commuting. I like the idea of a SportsCruiser for fuel consumption, speed, and avionics options. I would still use avgas in hot climates, and/or high density altitudes, though. A nice C152 would be cheaper cost of ownership. But, you will sacrifice speed. Considering hours are hours regardless of speed, time-building in a C152 might be worth it.

@Dean F.: Re cost of ownership, there's a wide range in car cost.  For instance, the Cadillac Escalades that my friend drives (when it's not in the shop, anyway) have a MSRP from =75K -95K, while the really reliable '02 Miata that I drive the most cost me under $5K.  Plenty of decent planes can be had for 70-90K :-)

No plane has these qualities, planes require a lot more servicing than cars both legally and practically. Similarly aircraft parts have service limits and heavily suggested rebuild times. Most if not all light aircraft require major servicing (or receive major servicing) at the 2000-2500ish hour mark.
There are comparatively little regulations on car maintenance. Most states require only a yearly inspection that boils down to a visual check of brakes, lights and a few other things as well as an emissions test mostly to keep the DEP happy.
Aircraft on the other hand require a verbose yearly "annual" inspection that can take days for a mechanic to complete. On top of that aircraft equipment needs to be routinely tested and checked for it to be legal for certain types of operation. On the contrary no one ever checks your cars speedometer or tach for proper operation.
Broadly speaking aircraft are also grounded if just about anything is not working where as most people often operate their car with small (or even large) issues. If you ever had an engine knocking issue in an aircraft you would be on the ground as fast as practically possible where as I know people that have driven cars thousands of miles with an "engine knock".
Airplanes also change substantially less than cars so small iterative fixes become difficult. If Toyota finds an issue in the 98 Corolla they can easily fix it in the 99 version. Fixing an airplane can require a lot of paper work, or if its a large issue an mandatory AD may be issued and everyone will be forced to fix it while 98 Corollas may still be out with their issues to this day.

If you just want a straight answer... A Piper Archer or a Cessna 172 (let the internet debates begin...)

Actually, most states don't require ANY inspection, other than emissions: https://en.wikipedia.org/wiki/Vehicle_inspection_in_the_United_States#Jurisdictions_requiring_periodic_vehicle_safety_inspections

@jamesqf i can only speak to the states I have lived in which have all required a minimum safety inspection but that is interesting.

I have an A&P friend/ co-owner who can sign of on the plane. I can park it in a field or on a lake at home. There must be a set upt that cost less than a car to fly to school then work in the long-run.

@Justintimeforfun: That's very much going to depend on the car you drive.  At a cruise setting, my Cherokee gets around 18 mpg.  IF you drive a large pickup or SUV, you can probably better this, more so if the route you drive is winding.  Not so if you drive a car that gets decent mpg.  Likewise, you can buy an older Cherokee or 172 for less that many upscale pickups & SUVS.  (And judging from a friend's experience with multiple Escalades, you might pay much less in maintenance :-))  Even better if you do have a realistic way to park the plane at home, or even at a small field near home.

@Justintimeforfun - What Jamesqf  says is exactly right about it depending on the car and plane compared. A Chevy and a Cadillac will have different costs for the same repair. Even if you do the repair yourself. Although, it is perfectly legal to save money by doing the repair yourself. And, you can get it done the same day. Not much you can do with a certificated aircraft. The OP is comparing a ‘98 Toyota Corolla. Hopefully, he can make repairs himself. Plus, hopefully, he is getting better than 20 mpg (highway) with the car. The plane should be a luxury. Not as your sole means of commuting.

Just because your buddy signs off on the work, still has to do the work. No there does not “must” be a way.  Aircraft are more expensive to own and maintenance is much more frequent and more expensive.  You might as well say “there must be a way to drive a Ferrari and get better MPG than my Corolla” - you can say it, but there isn’t.

@Harper - Reinstate Monica: It is definitely not the case that an airplane is ALWAYS more expensive. I spend less on the Cherokee - both purchase & maintenance - than a good many people spend on their cars.  (Though I also spend a lot less on my cars than they do.)  If you're a competent mechanic, you can also do much of the work yourself, under the supervision of an A&P.  For instance, I do all the time-consuming removal of access covers and so on, so my A&P just has to do the actual inspection.

@jamesqf this give me hope because I really donnot want to drive 15+ hours a week to school. Yes, I could just stay there, but I have a family. I really need something reliable, not to slow, and easy to fix/keep. Any ideas or concurrence?

@Justintimeforfun: I couldn't make any recommendations without knowing a lot more about your specific circumstances.  But I'd suggest looking at Trade-A-Plane to get an idea of current prices, consider the value of time-building to you, objectively judge your ability to maintain a plane, and so on.

@jamesqf It is really simple and maybe I should edit my post to reflect it. I need the cheapest plane I can build time on. The plane does not have to go 400 miles on a tank as long as I can land to refuel on the way.


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Are there all terrain landing gears for planes?
Is there a landing gear set up that will allow a single engine plane (also, allowing for tundra tires than what is not available for current water skids) to land on rough grass and water?
The wheels in the picture folds back to not case drag in the water; maybe the water-skid for a plane could work in this way for tundra tires?
Like this pictures landing skid but with tundra tires instead of those little ones.

Are you asking about bigger tires, or a retractable pontoon for water landings?  Because those are vastly different!  Definite yes on big tires, just google “tundra tires”.

Or are you asking about float planes with retractable wheels?  (Per your kayak photo). We need more clarity...

Related: are tracked landing gear systems still in use and developmen

@justintimeforfun, no, your edit did not clear things up.    Are you talking about landing on rough grass, or landing in water?  Landing on rough grass you want large tundra tires.  For landing on water, you need a pontoon float.  Are you asking about an amphibious plane that can do both?  Because these exist too.  Do a search on amphibious planes.  Otherwise you really need to clarify what you are asking.

Did you do a search on amphibious planes?  If so, did that answer your question?

Ok, so you already have a float plane and want to equip it with retractable Tundra tires?  What kind of plane?

@MichaelHall  Like the one I updated the question with.

Ok, now we are actually getting somewhere!  I have seen these take off from land quite a few times, but I have never seen one land.  I think you’d have a tough time stuffing larger tires in there, but I will let someone more knowledgeable answer.

The closest anyone has come to something that could be called a feasible all-terrain gear is the Air Cushion Landing System developed by Bell Aerospace and tested initially on a Lake Buccaneer, which lead to a test of a system Bell developed for the DeHavilland Canada DHC-5 Buffalo under a joint program between DH, the Canadian Govt, and the USAF.

The cushion was inflated by a pair of P&W PT-6 turboshaft powered inflation sytems (a kind of ducted fan setup), which are in the sponsons on each side of the fuselage.  The testing was completed in 1977.  I dimly remember that the biggest problem with the system was wearing out of the bottom surface of the cushion (it wasn't open like a hovercraft skirt, but more like an air mattress with an array of holes in the bottom, and the bottom surface would brush the ground and wear out really fast).  That and the obvious performance penalty issues (you're giving up a lot of payload to haul all that gear around) kind of killed it.
It could take off and land on any flat surface, and being a Buff, only needed a few hundred feet of space (the DHC-5 Buffalo could land and take off from a soccer field, and the normal version once did so in a civil defense demo in New York City, causing numerous calls by apartment dwellers to report the "crash" in a park).
I worked on this airplane as a mechanic when it returned from the test program to DH in 1979, removing the tip floats and the cushion system and patching the fuselage up before it was returned to its RCAF operating squadron.


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Is it possible that commercial airliners use an EMALS or other form of electric launch?
I am doing a big project for school over the summer, and was wondering if anyone can help? I just want a professional opinion on the idea. Is it possible or no?

Hello and welcome! Keep in mind that SE is not for help with homework questions. Do your homework (search), get a good idea, and only when you have specific narrow questions left, that can't be answered by search, ask here. As to your question, it's already been answered here: https://aviation.stackexchange.com/questions/31048/could-airliners-use-a-steam-or-electric-powered-catapult-for-take-off?rq=1

Even more specific is preferred here. A good question would include conditions like a timeframe (in 10 years or in 100?), your own research on the question (you looked it up and found out pros and cons...), and whether you wonder if it's possible there would be 10-20 EMALS airports in the world, in very special conditions (tiny mountaintops) or a widespread application. As to a brief opinion, without specifics, it's more of a "no", as the answers to the linked question this one duplicates mention.

@NATHANIELFOLEY It's not specific at all, and either "yes" or "no" would be a completely inadequate answer. Anything involving complex systems has many competing factors, which must be evaluated against each other. Any real answer is going to be of the lines "In certain circumstances, yes; in some other circumstances, no; then there are all the cases in the middle."

As a start I suppose the reason of that is a particular configuration where only a short runway could be build, for instance in a highly touristic island!
EMALS uses an electromagnetic linear motor operating on a track, some studies in the 50’s have been done in Europe using the same principle not to launch the train but as a continuous powering system however they were abandoned because of compatibility between countries.
As far as power is concerned, what was theoretically possible for a train could be possible to push or to pull an aircraft, but coming to the practical application, on which part of the aircraft the pushing or the pulling force shall be applied for launching; the landing gear presently available are not designed to accept such shear forces bringing the aircraft at least to V1.
If we consider the EMALS is just to reduce the runway length and is used just to bring an additional takeoff acceleration power, and supposing the location on the aircraft of the applied EMALS forces is solved, we get into another problem, that is the decision of the pilot at any moment before V1 to continue the takeoff or not? Should the pilot decide to cancel the flight, how to coordinate pilots decision with the EMALS disconnection, should it fail to disconnect the consequences could be terrific.
From my point of view this system requires specially designed compatible aircrafts, the economical feasibility can’t be general but specific to particular geographical configurations.
As a project why not? But economically it is hard to justify.

Thank you for such a helpful comment. It sparked an idea for my project ;)


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What is a "Standard visual inspection"?
Passengers injured as US fighter jet comes close to Iranian plane

The Iranian plane, belonging to Mahan Air, was heading from Tehran to Beirut on Thursday when the pilot staged a safety manoeuver, in an incident that Iran's Foreign Ministry said would be investigated. ... Central Command spokesman, said the F-15 "conducted a standard visual inspection of a Mahan Air passenger airliner at a safe distance of about 1,000 metres (3,280 feet) from the airliner this evening". "The visual inspection occurred to ensure the safety of coalition personnel at Tanf garrison," ... "Once the F-15 pilot identified the aircraft as a Mahan Air passenger plane, the F-15 safely opened distance from the aircraft." He added the intercept was carried out in accordance with international standards.

My questions are the following:

Is there such thing as "standard visual inspection" at all? Is it normal in such circumstances? What's its purpose and how necessary is it?
Isn't there any other method to this end, instead of "visual inspection"?
Is "1,000 metres" distance considered "safe" for such conditions?
In what conditions do passenger airliners stage a "safety manoeuver" like this?

Update

Are there similar incidents? Some military aircraft approaches an airliner to "inspect" it and see if it has really passengers on-board, in a manner they consider "safe" and "in accordance to international standards". The airliner considers this "unsafe" and stages a "safety maneuver", leading to injuries.

Is there such thing as "standard visual inspection" at all? Is it normal in such circumstances? What's its purpose and how necessary is it?
Visual inspections are very common. Military pilots train regularly to visual inspections of other aircraft, and typically close to within 25-50 feet of another (cooperative) aircraft to do so. At a 25-50 foot range, you can easily see if an aircraft panel is missing or even loose/flapping in the wind. Having said that, there is no "universal standard" for what comprises a safe and normal visual inspection and distances and closure rates that are considered safe may vary depending on your experience and aircraft type.
Isn't there any other method to this end, instead of "visual inspection"?
According to the researcher quoted in the article, the F-15 may have been attempting to see if the airliner had passengers onboard. You would need to close to well within 1/4 of a mile (1500 feet) to have any hope of determining that with a naked eyeball. If the F-15 had a camera system (common), that may have allowed them to remain farther from the airliner, however.
Is "1,000 metres" distance considered "safe" for such conditions?
1,000 meters is likely very safe, and it's really far away compared to how military pilots are trained. However, what matters is how the pilots of the airliner felt. They are likely not military trained, and were probably unaccustomed to seeing another aircraft that close to their airplane.
The article is a little misleading when it implies that aircraft typically maintain at least 600 meters separation to avoid hitting each other. That number (600 m), refers to two aircraft on different altitudes that not aware of the other's presence. For a military pilot who has a radar and is looking at an airliner, 600 m is not required at all.
In what conditions do passenger airliners stage a "safety manoeuver" like this?
Here's where we get into some speculation. I'm not sure what the article is referring to, but I suspect that the airline pilots were responding to a TCAS RA (Traffic Collision and Avoidance System- Resolution Advisory) generated by the F-15's proximity and closure rate to the airliner. In this case, the airline pilots may have been presented with a "Climb" or "Descent" command by the computer, which would explain their abrupt climb and descent.
Whether or not the climb they undertook should have been so violent that passengers were bounced out of their seat and onto the floor is a matter of the pilot's judgement and speculation without knowing exactly what happened between the two aircraft.

Thanks. I'm still trying to summarize this as "normal" in "such circumstances". Maybe I should clarify what I mean. Some military aircraft approached an airliner to "inspect" if it has really passengers on-board,  in a manner they considered "safe" and "in accordance to standards". The airliner considered this "unsafe" and staged a "safety maneuver". People were injured. So, assuming civilians' safety is considered in the "standard", it seems someone's action was not according to the "standard" here, and I guess your answer implies that it was the airliner's, not the F-15's, right?

And I understand what you mean by "there's no standard". I also understand the CentCom's statement about the "standard" is just their own judgement, based on circumstances. I wanna know if their judgement is valid enough. Maybe an example close to this situation here could help. I'll edit the question accordingly.

It seems like the question you're really asking is, "who is at fault here?" If you're willing to accept speculation, in my professional opinion: the airliner pilots wildly over-reacted. I would compare the airliner's reaction to a taxi driver who sees a police car turn on his lights as he drives across a parking lot toward the taxi. The taxi then swerves wildly to "avoid"  the police car and injures its passenger. It's not necessary - the police car was never going to hit the airliner.

It should be mentioned that sending fighters to intercept an airliner that stopped communicating to check whether the airliner has a problem and try to re-establish communication is fairly common. Most of the time the pilots simply set their radio incorrectly and quickly fix that error when they see the fighter, but if there is a bigger problem, the fighter can guide the aircraft to suitable airport. In this case the reason was slightly different, but the procedure used was basically the same, so it should be considered standard in that sense.

I find the claim that it was trying to check whether there are actually passengers rather difficult to believe, for two reasons: 1. the fighter didn't come close enough to really see and 2. even if there were few or none, it could still be a legitimate civilian flight, especially in this day of travel restrictions due to COVID. I think they were just verifying the type, tail number and livery match the plane they expected.

avherald reports that “the Mahan crew reacted to a TCAS resolution advisory to climb.” If that is confirmed, it was at least partly fault of the fighter pilot – they are supposed to switch their transponder to a mode that does not trigger TCAS when approaching the target and use their radar for separation instead exactly to avoid provoking it to abrupt manoeuvres.

@JanHudec Interesting. TCAS resolution advisory is what I suspected, but that still does not require maneuvers that bounce passengers out of their seats. TCAS resolution advisories expect a 0.25g acceleration within 5 seconds to a change of 1,500 feet per minute. Additional RA's require 0.35g within 2.5 seconds to an additional 2,500 feet per minute. Source: https://www.faa.gov/documentLibrary/media/Advisory_Circular/TCAS%20II%20V7.1%20Intro%20booklet.pdf

@Tyler, yes, TCAS RA indeed does not require bouncing passengers around and other crews react to them all the time without causing any injuries in the cabins. But every accident is a chain of issues and the fighter pilot not switching their transponder correctly for that kind of intercept is one of them.


text:
How do you request a "pop up" IFR clearance?
If you are flying VFR into deterioration weather conditions and would like to continue the flight under IFR, or you would like to climb to a better altitude but are restricted by a cloud layer, what is the easiest way to go about requesting and instrument clearance.

There is an excellent article on AvWeb about Pop-Up IFR which goes into more about when pilots should ask for a pop-up IFR clearance.  One of the most importatnt aspects is that if you are starting to get uncomfortable with the weather, or are being forced lower and lower, don't hesitate just because you aren't familiar with the proper procedure.
Obviously, you need to talk to ATC.  Find a frequency on your charts or from FSS.  If time is of the essence (you are in deteriorating VFR conditions and it's no better behind you) then ask for help on guard (121.5) rather than endangering yourself while looking for a frequency.  If the weather has gotten so bad that you are no longer able to maintain VFR or can no longer maintain safe terrain clearance, then start climbing immediately and contact ATC as soon as possible for help and a clearance.
More than anything else, be clear when you are in need.  Don't hesitate to declare an emergency if needed.  They really want to help you in this situation!  All of this applies, even if you aren't 100% legal for IFR flight if it can be done safely (i.e. just because your transponder hasn't received a 24 month inspection in time doesn't mean that you should just keep going lower until you end up clipping a tower).
All of that being said, asking for the clearance is done in pretty much the same way as asking for VFR flight following.  Tell them who you are, where you are, and what you need.  Their first priority when they get a request like this is to get you somewhere safe, and then they will ask you for additional information if they need it.

Asking FSS to get you a controller is a very good idea and easy to do.  They will basically tell you to ident and then call up the center/approach and ask whose scope you are flashing on and hand you off to them for services.

@abelenky, If you call me using only the aircraft ID, "Denver Center, N1234X", I'm writing down the callsign, and then typing in a database search to see if you've filed anything starting my airspace. If you haven't, I've still got my pencil ready for when I say, "N1234X, Denver Center, go ahead".
That's just a technique, of course, but my trainees do it, as well (or my ghost will haunt them).

Assuming you are not already talking to ATC:
You: Houston Center, Cessna 1234X, request*
Center: Cessna 34X, Houston Center, go ahead
You: Cessna 34X is a 172/U, 35 North IDU, 4500 ft, request IFR to Austin
Center: Cessna 34X ident, fly heading 270
Center: Cessna 34X is cleared to AUS via radar vectors, climb and maintain 6000 ft, squawk 5634
This is essentially the same as making a request for VFR flight following services with the exceptions:

Your aircraft needs to be legal for IFR.
You need to be rated and current for IFR.
You will receive a clearance.

If you already have flight following and need IFR, the controller has you on his scope and already has a strip for you, and you just need to ask him to make you IFR.  In that case he will just put you on an IFR altitude and give you a clearance limit and route.
*As noted in the comments, you may decorate this call with something identifying the nature of your request

Only thing I'd add is that on your initial call, you should say "Cessna 1234X, VFR, request".  Basically stating to ATC "I'm currently VFR, and you haven't heard from me before, so don't go looking for me in your flights or on your scope; You're not currently responsible for me."

That is a point of technique but may also misrepresent your intentions.  A controller may interpret that as a precursor to a flight following or other request for VFR services rather than a cold call for IFR services.  In practice I usually add my specific request to the end of that call e.g. request flight following or request popup IFR.

Fair point.  In that case, I think the short, simple, unambiguous call could be: "Center; Cessna 1234X, VFR; request IFR popup"

Maybe i'll ask this as a new question, but can ATC deny your request, and if so, what would be the next course of action.

If the request is denied you will be instructed to "maintain VFR".  If you have to have the clearance, indicate you need priority to the controller.  If you can maintain VFR and continue, do so and ask the next controller.  An IFR request is much less likely to be denied than a flight following request.  Another option if denied is to call FSS over VHF and file an IFR flight plan with them.  Then call back the controller to activate your flight plan.

You can also say that you need an immediate IFR clearance....  ATC isn't the only one that can use that term and it let's them know that you need priority.

The best way I've found to make an initial call to a controller who isn't handling me is: "Houston Center, good morning, Cessna 1234X...".  It's simple, quick, the controller always gets the message, and they always seem a little more friendly when they respond.  Controllers are people too.

Note that the AIM actually recommends adding "VFR" to your initial clearance request.  See this answer: http://aviation.stackexchange.com/a/1852/69


text:
Which languages are EASA exams and other documents available in?
Does EASA provide exams, documents and regulations only in English or in all the European Union Languages?
For example, I have to attend an exam for an EASA license. Can I do it only in English, or can I use another European Union language?

EASA creation regulation https://www.easa.europa.eu/system/files/dfu/approvals-and-standardisation-docs-syllabi-Syllabus_216_General_05032009.pdf
If it still doesnt work, search for "Regulation 216/2008"

@bogl I do not agree with you. The working language is the one used. The official language is the one (or the ones) ufficialy recognized as valid. I read from the answer: "applicants will not be disadvantaged in any way even if they use other official languages of the European Union." It is different from "to apply the only permitted language is english"

@bogl https://en.wikipedia.org/wiki/Official_language  An official language is a language that is given a special legal status in a particular country, state, or other jurisdiction.

I reworded your question to make it more specific, but it's possible that I changed the meaning too much. If my changes aren't good, please just reverse them or edit again.

@Pondlife it is not exactly the same meaning, but it is a consequence. So, I think now it is more clear and then it is an improvement anyway, thank you.

This post is an answer to the original question:

Which is EASA official language? English or all European Union Languages?

EASA communicates in English. They facilitate the translation of regulations to all member languages, but ultimately these translations are not within their domain of responsibility.
Therefore the official language appears to be English only.
See https://www.easa.europa.eu/the-agency/faqs/regulations:

Implementing Rules are available in all of the national languages of the EASA Member States. How is the quality of these translations assured? Who is responsible for the translations?
EASA is committed to facilitating the production of good quality translations. To ensure this and, where necessary, to improve, EASA has set up a Translation Working Group in 2008. This Working Group is made up of members of the National Aviation Authorities (NAAs), the Translation Centre of the EU Bodies (CdT), as well as EASA staff members. Also, EASA in cooperation with NAAs and CdT, is developing glossaries in the different aviation domains, such as Air Operations or Air Traffic Management, to enhance the quality of translations. The Member States also contribute to this project in order to capitalise on existing material and experience.
The final responsibility for translations lies with the EU Commission. The correction of translation mistakes of the Implementing Rules follows the same formal procedure as for their adoption: 1. preparation of the proposal, 2. interservice consultation, 3. committee, 4. scrutiny of European Parliament and of European Council, and 5. adoption. For minor mistakes, the procedure may be shorter. In any case, the linguistic changes will have to be agreed by the Commission’s translation services. These linguistic services will check that no substantial change is introduced, that the term used is acceptable according to an internal translation code or that the same change is included in all linguistic versions.

And here https://www.easa.europa.eu/the-agency/faqs/recruitment:

What language should I use in my application for a post at the Agency?
Applicants may use any of the official languages of the European Union when applying for a post advertised by the Agency. However, in order to speed up the selection process and to reduce the amount of the translations needed, applicants are invited to use English. Nevertheless, applicants will not be disadvantaged in any way even if they use other official languages of the European Union.
[...]
What language should I use in my application for a traineeship/study placement at the Agency?
A very good knowledge of the English language is an essential requirement to do a traineeship/study placement at EASA. Applications must therefore be submitted in English. For the same reason, the documents concerning traineeships and study placements at EASA are only available in English.

EASA does not issue licenses. That is the responsibility of the respective national aviation authority. In most European countries, examinees may choose to take their EASA license exams in either the local language or English.

Do you have any regulatori reference about that?

See https://www.easa.europa.eu/easa-and-you/general-aviation/licensing-general-aviation for the first two statements. Look at the information provided by flight schools for the latter. It depends on what kind of exam you want to take.


text:
What is the CPIOM in the IMA?
What is the CPIOM in the IMA architecture. Which is the difference between the CPIOM in the A380 and the CPIOM in the B777?

@ymb1 there is no reference to CPIOM in both question and answer.

In the IMA architecture, processing modules are hosted in a cabinet and are interconnected via a high speed bus. B777 uses "SAFEBUS" which is ARINC 659 on the backplane and ARINC 629 externally (same protocol, different physical layer). Airbus uses ARINC 664 internally and externally for the bus. Legacy bus interfaces go through an I/O module or other bus conversion interface.
The Airbus IMA contains 7 CPIOM (Core Processing & I/O Modules) that support both processing capability and I/O interfaces on a single module. It also includes one I/O Module (IOM) connected to the ARINC 664 bus for additional I/O.
The B777 AIMS cabinet contains Core Processing Modules (CPM) and separate I/O Modules (IOM).
The same functions exist in both, it's just that the Airbus CPIOM is a single module where B777 has two modules for the equivalent functionality.
And in a similar vein, the B787 IMA contains "GPMs" or General Processing Modules. It also contains two ARINC 664 network switches (network I/O for the cabinet). There are no direct legacy connections to the GPMs. Legacy (ARINC 429, CAN, discrete, analog) buses are connected to the external ARINC 664 network using Remote Data Concentrators (RDC).


text:
Does hypoxia affect pilots differently from people on the ground?
In my experience, many people don't have serious problems camping, skiing, hiking or doing other physical activities at 12,000 feet (3,600m).  We may get tired easily, and be out of breath, but we still function physically and mentally.
But for pilots (who aren't exerting themselves physically), hypoxia is a much more serious problem, e.g. see this article. Pilots aren't involved in heavy physical activity the same way mountaineers are, yet 91.211 requires O2 for periods as short as 30 minutes.
Is it accurate to say that hypoxia hits pilots harder than campers for some reason? Is there a clear reason why?

Maybe because pilot usually "shoot" up there compared to the others and may not have time to adjust.

The dangerous thing about hypoxia is that you are often not aware of how severely affected you are. Someone camping at high altitudes will probably not notice the extra fumbling needed to get the barbecue started or how finding direction takes a few seconds of extra thinking. In a cockpit, "fumbling" and "a few seconds" can mean the difference between life and death.

Hypoxia affects different people differently, and the FAA needed to be conservative with altitude restrictions for oxygen. People who are hiking/camping/skiing at 12k feet are usually active, athletic people who can adjust to that quickly. You need to take into account though the degradation in cognitive abilities, not just physical ones. There is also the problem of night/day. With oxygen deprivation, your eyesight degrades quickly at night.

Does the downvoter want to explain?  I think the question is cromulent.

Related: http://aviation.stackexchange.com/questions/30237/how-do-people-suffering-from-hypoxia-not-realize-they-arent-getting-enough-oxyg/

@abelenky  Did you mean cromulent?  Cromulent means appearing genuine but actually not.  A simpler word would help, especially with an international audience.

@Simon:  I'm using the Simpsons definition of cromulent.

@abelenky Whoops, sorry, I had been reading a couple of different questions regarding hypoxia and apparently confused them.

@abelenky Now I'm ashamed ;)

The analogy that if someone can become acclimated to working at high altitudes and therefore should not need supplemental O2 in an airplane is flawed. While flying - at least straight and level - does not require strenuous exertion, it is very cognitively taxing. It's a constant process if taking in a deluge of incoming data, be it instrument read outs, navigation information, external stimuli, radio chatter, the grunt work of flying the aircraft etc.
Unfortunately, the conscious and cognitive centers of the brain as well as the eyes require an oxygen rich blood supply in order to operate fully; if this is denied or reduced, serious deterioration of these abilities will occur and can happen rapidly within seconds.
Night vision is also severely impaired by hypoxia as the rods in your eyes require a lot of oxygen as well. I did an experiment one night in C172 where I took off at sea level and climbed to 12,500 feet. Looking outside the aircraft at those altitudes I could see a few bright stars but after I had landed back at close to sea level, I looked up at the night sky while tying down the airplane and could see a sky filled with stars as well as the bright gaseous strip of the Milky Way. The effect was dramatic; you really are affected by hypoxia at night.

I have heard of similar night experiments where a passenger at similar altitudes (12,500 feet) will then don an oxygen mask. Anecdotally, I have heard that it immediately increases brightness of stars and other lighted objects.

As far as the anecdote in the last paragraph, I wouldn't be so quick to chalk that up to hypoxia. While flying the airplane, your eyes will be adjusted to the light levels from the lights that are allowing you to read your instruments. When you're outside tying the plane down, your eyes will likely be adjusted to a lower light level unless there are bright lights around the ramp. Also, glass is partially reflective. You won't be able to see light sources on the other side of the glass that are less bright than the light reflecting off the inside of the glass from the panel and such.

I turned the panel light rheostats to the lowest possible setting where I could read the gauges in addition to turning off the wingtip strobes and allowed by eyes to adjust to the light levels.  The ramp was flooded with halogen light.  No there was a noticeable difference directly attributed to hypoxia.

@reirab Hypoxia begins to degrade your night vision at altitudes as low as 5000 feet.

Most people can function at 12,000 ft. Pilots do as well and don't need oxygen there.
Above that altitude, however, it gets worse very quickly. By 14,000 ft (where oxygen is always required for crew) most people will be noticeably short of breath and between 16,000 – 17,000 ft they may pass out.
I was once that high in the mountains. We were hiking, so some acclimatisation was taking place, though we were climbing faster then would be ideal. We first noticed being weakened as we neared the 13,000 ft. Then we spent two days there, so it got a bit better, but as we climbed above 15,000 ft, one (of the 15 or so) got altitude sickness and somewhere below 16,000 ft one had acute symptoms of hypoxia and had to turn back I think two of us turned back as we were barely able to walk. That matches the altitudes where pressurisation or supplemental oxygen is needed quite well.
Now if you get acclimatised, you will be able to function normally at those altitudes. That, however, requires spending days to weeks at the altitude. You'll never manage to get acclimatised just by flying.
Pilots acclimatised because they live at higher altitudes do handle the altitude better. But the regulations need to be simple and work for the worst case with some safety margin. Also, Carlo is right that brain requires a lot of oxygen, so concentration suffers even if you are not doing any physical exercise and don't feel physical weakness.


text:
What is a 709 ride?
One of the enforcement actions that FAA can take against a pilot is known as a "709 ride" in which your certifications and rating are reevaluated by the FAA.

What is the regulatory basis for this exam?
What are the possible outcomes of this examination?
When is this enforcement action used against a pilot?
What happens during a 709 ride? (maneuvers, oral examination, etc)

The regulatory basis for the exam comes from 49 USC 44709 (hence the name), which states:

(a) The Administrator of the Federal Aviation Administration may reinspect at any time a civil aircraft, aircraft engine, propeller, appliance, design organization, production certificate holder, air navigation facility, or air agency, or reexamine an airman holding a certificate issued under section 44703 of this title.

The outcomes and procedures are handled as show here.
Possible Outcomes (5-1424, 5-1428):
TL;DR: As shown in 5-1428, the results are:

Issuance of a letter of results to the airman;
Possible issuance of a Temporary Airman Certificate; or
Possible downgrade of the airman’s certificate.

If the airman satisfactorily completes the reexamination (5-1424(A)), then the inspector will issue a letter of results. If the certificate had been temporarily suspended, then the FSDO forwards a copy of the letter of results to the Regional Assistant Chief Counsel, who then takes appropriate action to terminate the suspension. If the airman needs use of the certificate immediately, the Regional Assistant Chief Counsel may authorize the inspector to issue a temporary certificate that bears all ratings and limitations from the original certificate. Otherwise, if the certificate had not been suspended, the airman is free to exercise the privileges of the certificate and/or ratings.
If the airman does not satisfactorily complete the reexamination (5-1424(B)), then:

The airman must be informed in detail of each deficiency. Additionally, if the airman’s certificate had been temporarily deposited at the FSDO and the temporary deposit term is nearing expiration, a decision must be made to suspend the certificate or to extend the temporary deposit period for another 30 days. If, in the opinion of the inspector, the airman could successfully complete another reexamination by obtaining additional instruction, every effort must be made to encourage the airman to do so.

Depending on what the inspector decides, one of two things happens:

1) When the inspector decides to allow the airman additional time, the inspector takes the airman's certificate for temporary deposit at the FSDO and issues a temporary certificate. The temporary certificate must have a limitation against carrying passengers and a 30-day expiration date. The airman has 30 days in which to practice or obtain additional dual instruction before being reexamined again.
2) If the inspector determines the airman is unable to establish qualification to hold the certificate or rating, legal enforcement action must be taken to revoke the airman’s certificate and/or ratings. (See FAA Order 2150.3, Chapter 8.)

When is the enforcement action issued?
This is mostly covered in the above sections. Essentially, if you are not found deficient, a revocation of your suspension will begin to be processed or you can just proceed on your merry way. If you are found deficient, then you will either be immediately be issued a temporary certificate with limitations so you can practice to pass another re-exam, or your certificate will revoked as soon as can be legally done (presumably the inspector will tell you not to fly, but I don't have backing for that).
What happens during a 709 ride? (5-1423)
Part (A) of 5-1423 deals with this, and states:

Extent of Reexamination. The inspector should test the airman only in the areas specified in the letter of notification. However, if other deficient areas are noted during the reexamination, these would also be the basis for failure of the test. For example, during a reexamination when the airman was to be tested on the ability to recognize and recover from stalls, the inspector noted that on takeoff the airman over-rotated to a dangerously high pitch attitude, requiring the inspector to take corrective action. In this situation the reexamination should be discontinued, and the airman should be informed of failing the test because of deficient skills exhibited while en route to demonstrate the maneuvers.

Part (B) notes that the inspector can place special emphasis on certain areas based on the reason for the letter being issued. You can fail if you are unqualified for any maneuver contained in the PTS for the certificate/rating you are being tested for, as Part (C) notes.
Part (D) notes that the test does not have to be flight-based, though presumably one that did would have some portion of oral examination. (Part (E) allows the test to be taken in a simulator, if it is requested by the airman and approved by the inspector).

Knowledge Reexamination. The reexamination may be conducted using an oral or knowledge test, devised by the inspector, if the area to be reexamined is one of knowledge rather than skill or flight proficiency.

Reference: http://www.law.cornell.edu/uscode/text/49/44709
The regulatory basis appears to be 49 U.S. Code § 44709 - Amendments, modifications, suspensions, and revocations of certificates
When might a 709 ride happen:

The Administrator of the Federal Aviation Administration may reinspect at any time a civil aircraft, aircraft engine, propeller, appliance, design organization, production certificate holder, air navigation facility, or air agency, or reexamine an airman holding a certificate issued under section 44703 of this title.

Generally only as the result of some (alleged) violation. I've found references to CFIs receiving 709's as a result of actions performed by not only their students, but former students as well.
Possible outcomes:

The FAA may amend, modify, suspend, or revoke the certificate in question.

What happens:
I haven't found a definitive source to this but rather anecdotal evidence to suggest the pilot being examined is subject to the PTS of the certificate in question, but this is not to imply that a full check ride will be required. Rather, the extent of the examination is up to the inspector.

Yes, he is subject to the PTS of the certificate in question (see the very end of my answer), and the examination is up to the instructor